linefit.py

# ##### BEGIN GPL LICENSE BLOCK #####
#
#  LineFit, (c) 2017, 2024 Michel Anders (varkenvarken)
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU General Public License
#  as published by the Free Software Foundation; either version 2
#  of the License, or (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software Foundation,
#  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
#
# ##### END GPL LICENSE BLOCK #####

bl_info = {
    "name": "LineFit",
    "author": "Michel Anders (varkenvarken)",
    "version": (0, 0, 20240119100755),
    "blender": (4, 0, 0),
    "location": "Edit mode 3d-view, Add-->LineFit",
    "description": "Add a single edge to the mesh that best fits a collection of selected vertices",
    "warning": "",
    "wiki_url": "",
    "category": "Mesh",
}

import numpy as np


def lineFit(points):
    ctr = points.mean(axis=0)
    x = points - ctr
    M = np.cov(x.T)
    eigenvalues, eigenvectors = np.linalg.eig(M)
    direction = eigenvectors[:, eigenvalues.argmax()]
    return ctr, direction


import bpy


class LineFit(bpy.types.Operator):
    bl_idname = "mesh.linefit"
    bl_label = "LineFit"
    bl_options = {"REGISTER", "UNDO"}

    size : bpy.props.FloatProperty(
        name="Length",
        description="Length of the line segment",
        default=1,
        min=0,
        soft_max=10,
    )

    @classmethod
    def poll(self, context):
        return context.mode == "EDIT_MESH" and context.active_object.type == "MESH"

    def execute(self, context):
        bpy.ops.object.editmode_toggle()
        me = context.active_object.data
        count = len(me.vertices)
        if count > 0:  # degenerate mesh, but better safe than sorry
            shape = (count, 3)
            verts = np.empty(count * 3, dtype=np.float32)
            selected = np.empty(count, dtype=np.bool)
            me.vertices.foreach_get("co", verts)
            me.vertices.foreach_get("select", selected)
            verts.shape = shape
            if np.count_nonzero(selected) >= 2:
                ctr, direction = lineFit(verts[selected])
                # can't use mesh.from_pydata here because that won't let us ADD to a mesh
                me.vertices.add(2)
                me.vertices[count].co = ctr - direction * self.size
                me.vertices[count + 1].co = ctr + direction * self.size
                ecount = len(me.edges)
                me.edges.add(1)
                me.edges[ecount].vertices = [count, count + 1]
                me.update(calc_edges=False)
            else:
                self.report(
                    {"WARNING"},
                    "Need at least 2 selected vertices to fit a line through",
                )
        bpy.ops.object.editmode_toggle()
        return {"FINISHED"}


def menu_func(self, context):
    self.layout.operator(LineFit.bl_idname, text="Fit line to selected", icon="PLUGIN")


def register():
    bpy.utils.register_class(LineFit)
    bpy.types.VIEW3D_MT_mesh_add.append(menu_func)


def unregister():
    bpy.types.VIEW3D_MT_mesh_add.remove(menu_func)
    bpy.utils.unregister_class(LineFit)


if __name__ == "__main__":
    register()